1. Field of the Invention
The present invention relates to a motor control device for controlling operation of a motor. The present invention also relates to a motor drive system and electrical equipment that utilizes the motor control device.
2. Description of Related Art
Conventionally, there exists already developed technology to detect a magnetic pole position (a rotor position) at a rotor of a motor without utilizing a position sensor. Such technology includes utilizing the application of a high-frequency rotation voltage or alternating voltage.
The applicant also previously proposed a method utilizing application of a high-frequency voltage (see Japanese Patent Laid-Open No. 2007-53829). In this method, estimated axes for control corresponding to a d-axis and a q-axis are set as a γ-axis and a d-axis respectively, and a high-frequency rotation voltage or alternating voltage on the γδ coordinate system is applied to a motor. A magnetic pole position is estimated based on a derived product of γ-axis and d-axis components of a high-frequency current that flows through the motor due to application of the high-frequency voltage.
In this conventional method, an axial error Δθ is estimated under the approximation that the axial error Δθ between the d-axis and the γ-axis as an estimation axis is close to zero, and therefore, it is necessary that the γ-axis as an estimation axis and the d-axis corresponding to the magnetic pole position coincide with each other. Thus, depending on the initial position of the estimated axis, that is, depending on the initial axial error Δθ, there may be an instance in which the estimation takes a certain amount of time. Reasons for this will become more apparent by referring to the description in the embodiments of this invention.
If it takes a certain amount of time to estimate the initial magnetic pole position when trying to start a motor, it will take about that much time to start the motor as well. Delay in starting the motor leads to delay in starting the equipment in which the motor is installed such as an electric vehicle. Therefore, it is desired that the time required for estimating the magnetic pole position be shortened or minimized.
Therefore, an object of the invention is to provide a motor control device, a motor control system, and equipment which contribute to shortening the time required in estimating the magnetic pole position (the initial magnetic pole position) to control operation of a motor.